Throughout the world, third-generation mobile services are being introduced. As a consequence, a plurality of different radio access technologies (RAT) coexists, e.g. TDMA, WCDMA, CDMA2000, WLAN etc.
In order to enable almost seamless services for the end-users, third generation mobile terminals are equipped with so called dual RAT, e.g. both WCDMA (Wideband Code-Division Multiple Access) and GSM technology (Global System for Mobile communications) i.e. TDMA, whereby the mobile terminal is able to communicate with both RATs. Likewise, the mobile terminal and the radio access network have to be able to support handover between the two technologies.
Handover between networks utilizing different RAT require that a dual-mode user equipment or mobile terminal, while communicating over a first radio access network utilizing a first RAT, perform measurements on neighboring cells in a second radio access network utilizing a second RAT.
Depending on the type of network, either the mobile terminal itself decides when to change from one cell to another, or the decision is performed at a network node such as a base station controller in the first network. The later case suggests that the mobile terminal has to report some measured parameters to a base station.
During handover from a GSM network to a network utilizing WCDMA e.g. UTRAN, the mobile transmits a standardized measurement report to the base station controller of the GSM network. Consequently, the base station controller, based on the received measurement report, decides to which target UTRAN cell the handover will be effected.
Various problems are associated with such inter-RAT handovers, typically due to the inherent differences in the radio access technologies.